1. Field of the Invention
The present invention relates to an anode for molten carbonate fuel cell and a molten carbonate fuel cell (hereinafter, it is referred to as MCFC) containing the same. In particular, the present invention relates to an anode for MCFC and a MCFC containing the same to maintain stably excellent cell performances during a long drive by preventing electrolyte loss by improving wettability of the MCFC against the electrolyte, which is accomplished by coating the internal surface of the anode pore with a porous ceramic film.
2. Description of the Related Art
A preferable material of an anode for MCFC should satisfy high conductivity, excellent catalytic activity for oxidation of hydrogen (H2), high porosity, improved resistivity (stability) against sintering and creep, proper wettability against molten carbonate, and finally low price. However, when MCFC is operated during an extended period of time, the molten carbonate of electrolyte is always gradually lost due to evaporation of the electrolyte or corrosion of the dividing plate. In consequence, the amount of impregnated electrolyte of matrix decreases, causing cross-over between the fuel and the oxidizer, and the stability of MCFC performances during an extended period of time is much difficult to obtain.
In order to solve the problems described above, a number of attempts have been made. One method incorporates a large amount of electrolyte in anticipation of a lot of consumption of the molten carbonate of electrolyte of the MCFC. However, if too much electrolyte is supplied, it first flows into a cathode that has a relatively good wettability to an anode, and consequently deteriorates the cell""s performances, causing a flooding phenomenon. To prevent the flooding occurrence, the anode should have very small pores that trigger capillary pressure difference in the cell, which in turn increases the amount of the impregnated electrolyte in the anode, or the wettability against the electrolyte of the anode should be greatly improved. However, when the pores of the anode are considerably small, diffusion resistance of a reactant gas occurs, and the electrodes are severely polarized thereby, and in result, the ability of the cell is weakened. In addition, considering that different materials have their own wettability, the wettability of the material is improved only when the surface of the material is comprehensively modified. Unless the surface is modified, the anode material or the electrolytic material should be changed instead. However, a method for improving the wettability of the anode without changing the anode material or the electrolytic material itself is needed. In view of the foregoing, the MCFC anode having high porosity and excellent wettability against the electrolyte even in case of using a conventional anode material and the electrolytic material at a constant pore size should be developed.
Other methods for improving MCFC""s performances have been continuously suggested. In the early stage of the MCFC development, for example, Ag or Pt was the typical anode material. However, in consideration of conductivity, catalytic activity and cost, Ni or an alloy of Ni and Cr is being widely used now. Frequently used methods in the art for improving MCFC performances include a method of electroless plating the oxide by Ni or Cu, a method of adding an oxide like LiAlO2 or Al2O3 to Ni, a method of solution impregnation to form an oxide in a final stage of the operation by impregnating a salt solution, and a method of using an Ni-based alloy, such as, Nixe2x80x94Cr or Nixe2x80x94Al. Despite of many trials, the methods aforementioned could not achieve significant improvement on the wettability of the anode against the electrolyte, because in a way, they are only for improving sintering and creep resistance of the anode, sporadically forming little oxide particles on the anode.
In addition, Kunz et al (U.S. Pat. No. 4,596,751) discloses a method of changing the amount of the impregnated electrolyte by differentiating the sizes of pores of a cathode, a matrix and an anode. However, the method should be applied with caution in that the size control of pores of each cell component is directly related to the porosity and the cell performance with each other. Accordingly, the method is again insufficient for significantly increasing the amount of the impregnated electrolyte.
Although many attempts have been made to increase the amount of the impregnated electrolyte for the MCFC anode, the results are not very satisfactory in terms of improving the impregnation of electrolyte. Therefore, it is necessary to develop a method for increasing the amount of the impregnated electrolyte with an easy control over microstructure and simplified process without using expensive reactant or equipment.
It is, therefore, an object of the present invention to provide an anode for a molten carbonate fuel cell (MCFC) with improved wettability and an amount of impregnated electrolyte, so that a cathode of the cell is not flooded due to oversupplied electrolyte, and electrolyte loss and deterioration of cell""s performance due to evaporation and corrosion of the molten carbonate during long periods of operation of MCFC are successfully prevented.
Another object of the present invention is to provide an anode for the MCFC to prevent gas diffusion resistance of the anode by maintaining microstructures without changing the size of pores of the anode, so that the MCFC can be operated for an extended period of time, yet maintaining a good stability without any electrolyte loss.
To achieve the above object, there is provided an anode for a MCFC including an anode, electrolyte and a cathode, wherein the anode has pore""s surfaces coated by a porous ceramic film.
The anode material for the MCFC is selected from a group consisting of pure Ni, metallic mixtures containing Ni, alloys containing Ni, and metallic compounds containing Ni.
Preferably, the porous ceramic film for coating the anode for the MCFC is selected from a group consisting of aluminum oxide sol, cerium oxide sol, zirconium oxide sol, aluminum hydroxide sol, cerium hydroxide sol and zirconium hydroxide sol.
At this time, the porous ceramic film of the MCFC anode is formed through a sol-gel process, which dips the anode into a ceramic sol, and then dries.
The coating process usually takes less than 1 minute.
Also, the coating process of the anode for the MCFC is repeated more than once.
Preferably, in the present invention, the coating process of the anode for the MCFC is repeated twice.
Preferably, the amount of the coating is in a range of from 4 to 5% by weight based on the total weight of the anode.